Expo app works in simulator, crashes on a real iPhone at startup

Answering my own question for the next person: the crash was a missing NSCameraUsageDescription in app.json. iOS kills the app the moment a permission is requested without a description, and the simulator does not.

How to see it: Xcode → Window → Devices → your phone → "Open Console", filter on your app name. The crash reason is in there in plain English.

Good catch. For others: npx expo-doctor flags most of these before you build.